1. Field of the Invention
The present invention relates to a fastener means comprising a male fastener which is provided with a permanent magnet and a female fastener which includes an engagement means to be attracted to the permanent magnet of the male fastener when the male fastener is inserted into the female fastener, the engagement means being adapted to become engaged with said male fastener when it is attracted by the permanent magnet, and more particularly to a fastener means wherein a portion on one side of the engagement means is made of non-magnetic or weakly magnetic material.
2. Prior Art
Fastener means comprising a male fastener with a permanent magnet and a female fastener provided with a ferromagnetic slide plate which engages with a projection on the male fastener are used for various purposes, such as for backpacks to fasten the cover to the body or in shoulder bags to keep the cover closed.
Fastener means of this type have been proposed in a number of patent applications such as Japanese Patent Application (JPA) No. Sho57-128,762, JPA Hei3-244,067, JPA Hei3-246,466, JPA Hei4-177,725 and JPA Hei4-180,407. These fastener means are characterized in that by merely inserting a projection provided on the male fastener into the female fastener, a slide plate provided on the female fastener is attracted by the permanent magnet on the male fastener and easily secures engagement of the male and the female fasteners. In this type of fastener means, however, the slide plate in the female fastener to be magnetically attracted and become engaged with the projection on the male fastener is made of a ferromagnetic material shaped substantially as a square with a square hole, into which the projection of the male fastener is inserted.
In order to conveniently and firmly attract and engage the slide plate on the female fastener with the permanent magnet provided at the projection of the male fastener, it is necessary to provide a hole on the slide plate at a position slightly closer to the projection. Normally, the opposite side of the slide plate is disposed at a distance from the projection.
For this purpose, the slide plate is usually shaped like a frame with a large opening. This results in a slide plate which is considerably larger as relative to the size of the projection of the male fastener to be inserted, making it difficult to reduce the size of the female fastener.
Another defect of this particular construction of the slide plate is that the plate tends to become fragile and fails to slide stably inside the female fastener. Moreover, the frame-shaped slide plate constitutes a magnetic path even on the side where it is not magnetically attracted. This leads to a magnetic leakage and reduces the force of the projection to attract the slide plate for the amount corresponding to that leakage. Additional disadvantage is that a magnetic circuit for the permanent magnet is formed at a portion where the slide plate is manipulated.